1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to wireless networking and transmitting and receiving data in the wireless network, and more particularly, to a wireless network system and a method for transmitting and receiving data in the wireless network, which have a particular time period for a beam search in a superframe thereof in order to enable stations, which carry out directional communications with a high frequency bandwidth, to efficiently perform a beam search.
2. Description of the Prior Art
FIG. 1 is a view illustrating a half-duplex wireless network which adopts conventional Request-To-Send and Clear-To-Send signals.
Generally, a wireless network adopts a half-duplex scheme by which it is impossible to simultaneously perform transmission and reception. While accessing wireless media by using the half-duplex scheme, a Request-To-Send (RTS) signal 111 and a Clear-To-Send (CTS) signal 121 are used in order to prevent collision due to media possession.
A sending station 110, which has frames to be transmitted, transmits an RTS signal 111 to start a transmission procedure, and all neighboring stations which have received the RTS signal 111 stop generation of radio waves. Upon receiving the RTS signal 111, a receiving station 120 responds to the RTS signal 111 by means of the CTS signal 121, which in turn makes all neighboring stations stop to generate radio waves. The sending station 110 which has received the CTS signal 121 transmits a frame 112 and then receives an acknowledgement signal 122 from the receiving station 120 which has received the frame 112.
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), which is a Media Access Control (MAC) algorithm generally used under the circumstances of wireless Local Area Network (LAN), is provided by Distributed Coordination Function (DCF) which, as in Ethernet, examines whether a wireless link is clear before the sending station 110 transmits the frame 112, and which uses any back-off at the time of an end of respective frames 112 in order to avoid collision with other stations.
A carrier sense function is used to determine whether transmission media are available, and is classified into a function for physically sensing the carrier and a function for virtually sensing the carrier. The function for physically sensing the carrier is provided by a physical layer, and depends on an adopted medium and an applied modulation scheme. The function for virtually sensing the carrier is provided by Network Allocation Vector (NAV), wherein the NAV corresponds to a timer which implies time information in a case where media have been reserved. Herein, the NAV is included in and transmitted by frame headers of the RTS signal 111 and the CTS signal 121, and both the sending station 110 and the receiving station 120 set times, which are necessary to complete their operations, to the NAV to prevent other stations from using the media.
Meanwhile, under the circumstances of the wireless Personal Area Network (PAN), timing is based on a superframe.
FIG. 2 is a view illustrating a conventional superframe, wherein the superframe 200 includes a beacon period 210, a contention access period 220, and a channel time allocation period 230.
The contention access period 220 is used to transmit or receive asynchronous data or a control command. The channel time allocation period 230 includes a Channel Time Allocation (CTA) 232 and a Management Channel Time Allocation (MCTA) 231, and is used to transmit or receive a control command, isochronous data or asynchronous data.
The length of the contention access period 220 is determined by the access point, and is transmitted to the stations, which constitute a network, by beacon frames which are distributed to the beacon period 210.
During the contention access period 220, the above CSMA/CA is used as a media access scheme. During the channel time allocation period 230, a Time Division Multiple Access (TDMA) scheme, which has a specific time window for each station, is used. Here, the access point allocates a channel time period to an apparatus which requests an access to media, and transmits data to or receives data from the relevant station during the allocated channel time period. Herein, the MCTA 231 is allocated to a pair of stations which are to transmit data to or receive data from each other, and is used as a common CTA which gains access by Time Division Multiple Access (TDMA) or which uses a Slotted Aloha protocol.
Along with the scheme by which compressed data is transmitted using a bandwidth of several Gbps, another scheme by which uncompressed data is transmitted using a bandwidth of several tens of Gbps is being tested. The uncompressed data, the volume of which is larger than that of the compressed data, can be transmitted only using a bandwidth of several tens of Gbps. In the case where packets are lost during data transmission, not compressing the data has a less of an effect on the output of the data than compressing the data.
Transmission or reception of data with a high frequency bandwidth can be carried out via directional communication. In the case where the directions of both stations are different from each other, the packets could be lost. Therefore, both stations have to change the direction of communication while they communicate with each other to perform a beam search. In the case where beam searching is to be carried out, if a communication medium is being used by other stations or a coordinator, it may be impossible to perform the beam searching.
Therefore, there has been a request for a technology which can facilitate the beam searching between the stations.